The development of mining activities in North Chile involves a great number of workers intermittently exposed to high altitude for a long period of time (chronic intermittent hypoxia, CIH). A 2(1/2)-year prospective study aimed to characterize this model of exposure to CIH and to know whether this condition may progressively lead to a chronic pattern. Twenty-nine miners, aged 25 +/- 5 yr, working 7 days at HA (3800 to 4600 m) and resting 7 days at sea level (SL) were studied. Subjects underwent a physical examination, EKG, hematological status, maximal exercise test, ventilatory and cardiac response to hypoxia (F(iO2) = 0.114) at rest and exercise, pulmonary vascular response to hypoxia by echocardiography, and 24-h monitoring of EKG and arterial pressure. Basal evaluations were performed at SL before the first exposure to hypoxia. HA measurements were daily AMS score, sleep status, and 24-h monitoring of EKG and arterial pressure. All these measurements were repeated after a mean period of 12, 19, and 31 months. Hematocrit increased but reached values lower than those observed in chronic permanent exposure. Systemic and pulmonary arterial pressures measured at SL did not change, but were higher in hypoxia. Right ventricle showed a slight dilatation. Exercise performance at SL declined with exposure to CIH to reach a 12.3% decrease after 31 months of CIH, associated with a 6.8% decrease in maximal heart rate. Signs of ventilatory acclimatization were observed after 12 months. Symptoms of AMS and sleep disturbances were still seen on the first 2 days at HA, whatever the time of exposure to CIH. In conclusion, CIH induced a clear acclimatization process. Subjects did not reach a health status comparable to that seen in permanent residents at HA and remained at risk of acute altitude-induced illnesses.

In the past two decades, Chile has developed intense mining activity in the Andes mountain range, whose altitude is over 4,000 meters above sea level. It is estimated that a workforce population of over 55,000 is exposed to high altitude hypobaric hypoxia. The miners work under shift systems which vary from 4 to 20 days at the worksite followed by rest days at sea level, in a cycle repeated for several years. This Chronic Intermittent Hypoxia (CIH) constitutes an unusual condition for workers involving a series of changes at the physiological, cellular and molecular levels attempting to compensate for the decrease in the environmental partial pressure of oxygen (PO 2 ). The mine worker must become acclimatized to CIH, and consequently undergoes an acute acclimatization process when he reaches the worksite and an acute reverse process when he reaches sea level. We have observed that after a period of 3 to 8 years of CIH exposure workers acclimatize well, and evidence from our studies and those of others indicates that CIH induces acute and chronic multisystem adjustments which are eff ective in off setting the reduced availability of oxygen at high altitudes. The aims of this review are to summarize fi ndings of the physiological responses to CIH exposure, highlighting outstanding issues in the fi eld.

Our results indicate that children are extremely sensitive to hypoxia, as expressed by symptoms of AMS and significant desaturation. Our findings add to the available information regarding the problems encountered when ascending to high altitude with children and support the importance of close monitoring of young children during ascent to high altitude.

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